Upon receipt of a petition asking that a zone be created, or upon motion of the board, the board shall adopt a resolution which shall describe the boundaries of such proposed zone; describe in general terms the flood control needs or requirements within the zone; set a date for public hearing upon the creation of such zone, which shall be not more than thirty days after the adoption of such resolution. Notice of such hearing and publication shall be had in the manner provided in RCW 36.32.120(7).

At the hearing scheduled upon the resolution, the board shall permit all interested parties to be heard. Thereafter, the board may reject the resolution or it may modify the boundaries of such zone and make such other corrections or additions to the resolutions as they deem necessary to the accomplishment of the purpose of this chapter: PROVIDED, That if the boundaries of such zone are enlarged, the board shall hold an additional hearing following publication and notice of such new boundaries: PROVIDED FURTHER, That the boundaries of any zone shall generally follow the boundaries of the watershed area affected: PROVIDED FURTHER, That the immediately preceding proviso shall in no way limit or be construed to prohibit the formation of a countywide flood control zone district authorized to be created by RCW 86.15.025.

Within ten days after final hearing on a resolution, the board shall issue its order.